Time division multiplex telephone system



Jan. 20, 1948. J. H. HOMRIGHOUS 2,434,698

TIME DIVISION MULTIPLEX TELEPHONE SYSTEM Filed Feb. 15, 1944 s Sheets-Sheet 1 m m m m Filmllllll l|| 7 n n/ 4 llllll lllll ll 3 4 n J 4 a E a 2 2 vm l z 4 MAT m u If .3 2.. n F I l n I X W im .W /m EL 4 7 I w G {a w 3 m H I I ll: l||| l 97 I 2 7| b h 3 Jan. 20, 1948.

J. H. HOMRIGHOUS TIME DIVISION MULTIPLEX TELEPHONE SYSTEM Filed Feb. 16, 1944 3 Sheets-Sheet 2 INVENTOR.

z: 15o 43 144 Mo .y E f FIG 5 Jan. 20, 1948.

, J. H. HOMRIGHOUS TIME DIVISION MULTIPLEX TELEPHONE SYSTEM Filed Feb. 15, 1944 5 Sheets-Sheet 3 IN V EN TOR.

Patented Jan. 20, 1948 UNITED STATES PATENT OFFICE TIME DIVISION- MULTIPLE); TELEPHONE SYSTEM John H. Homrighous, Oak Park, Ill. Application February 15, 1944 Serial No. 522,475;

Claims. 1

This invention relates to an improved multiplex telephone system and more particularly to a system for increasing the number of messages that may be transmitted over trunk lines.

One of the objects of my invention is to provide means for transmitting two messages simultaneously over a phantom circuit.

Another object of the instant invention is to provide means for transmitting two messages simultaneously over a phantom circuit, and also for transmitting two messages at the same time over each of the physical trunk lines utilized for the phantom circuit,

Another object of my invention is to provide an improved two message two-way mechanism for reducing and expanding the period of time for small portions or, fragments of messages.

Another object of this invention is to provide synchronizing or control signals from a master generator over pilot wire circuits or trunk lines to the various telephone ofiices in the system, whereby, all the two message two-way mechanisms in the system may be controlled in time relation by the master generator.

Another object of the instant invention is to provide means in a two message two-way transmission trunk line for signaling the operator in either direction independently for either message.

Another object of the instant invention is to provide means in a two message two-Way phantom group of trunks for signaling the operator independently for each message in either direction over the two physical trunks, and'over the phantom circuit.

Still another object of the instant invention is means for associating the message reducing and expanding mechanism with the operators cord circuits rather than with the trunk lines.

Several telephone messages may be transmitted simultaneously over a pair of conductors by providing a different carrier wave for each telephone message, or two different messages may be transmitted over a trunk line by reducing the period of time for equal portions of different messages and transmitting these portions by twenty-four volt power and forty-eight volt poWer in rotation. In the instant invention I separate the sound signals for two messages into equal portions or fragments and reduce the period of time for each portion approximately one half and synchronize the transmission and the reception of difierent messages in all the telephone offices by control signals developed by a master generator in one ofiice and transmitted over trunk lines to all other ofiiees i th sys Other objects will be apparent from the followingdescription taken in connection with the accompanying drawings in which:

Figure 1 is a schematic of a trunking system between telephone offices and cities.

Figure 2 is a block diagram illustrating a cir; cuit' arrangement for interconnecting telephone. subscribers.

Figure 3 shows a two message two-way transmissions trunk line.

Figure 4 shows a'multi message two-Way transmission phantom trunk group.

Figures 5 and 6 show cord orlink circuits for interconnecting trunk lines and subscriberslines.

Figure 1 represents a telephone trunking arrangement between several telephone oflices l to 6 inclusive. The telephone oflices I, 2. and 3 may be in the same city I while the ofiices 4, 5 and 6 may be inother towns or cities 8, 9 and 10. The solid lines between these telephone ofilces repree sent a group of trunk lines, while the dash lines represent pilot wire or trunk lines for transmitting control signals from the master generator I l in 'ofiice I; The lines [2 and I3 may represent groups of two message two-way transmission trunks. The line H and It: may represent two different types of trunks; l4. may be'a group of two message two-way transmission trunks, and [5 may represent phantom groups for multi message two-way transmission. l6 and I! may be two message two-way transmission groups, while l8 may represent phantom groups similar to IE.

The master generator at H may develop control signals of sine wave form, and from this generator the signals of sine wave form may be trans,- mitted over separate trunk lines such as [9, 29 and 2! to the designated offices in the different towns and cities. In oflice 8 the signals may be amplified and relayed over trunk 22 to another ofiice, The sine wave signals after being amplified in each office are changed to square waves and utilized to synchronize the message reducing and expanding mechanism with the home or originating office.

Figure 2 represents the trunking arrangement and the cord circuits used for interconnecting the subscribers in the telephone ofiices l, 4 and 5. The subscribers telephones 23, 24 and 25 are of a conventional type well known in the art. The numerals 26, 21 and '28 may represent the conventional line and out off relay and signals associated with the subscribers lines. The double blocks 29 and 30 represent the apparatus associated with each end of the trunk line. each comprising two jacks, two lamps, tWQ line relays, two out off re lays, and a signal control relay for the transmissions and reception of two intelligence messages simultaneously. Cord or link circuits 3| and 32 and other similar circuit may be utilized for connecting two subscribers in ofiice I to two subscribers in ofiice 4 through the trunk line 33, which may be one trunk in the group Hi. The cords 3| and 32 comprise message reducing and expanding mechanism for changing the period of time for successive fragments of the messages.

The phantom groups 34 comprises two pairs of conductors 35 and 36 with a phantom circuit 3'! superimposed in conventional manner upon the two pairs of conductors or the two physical circuits. The double blocks 33 and 39 represent the apparatus associated with each trunk circuit, each block comprising two jacks, two lamps, two line relays, two out off relays, one signal control relay, and associated circuits for the transmission and reception of two messages over each trunk circuit. Cord circuits 3| and 32 may be employed as before to interconnect subscribers in offices l and 4, Now suppose that the subscriber at 23 is Calling the subscriber 25 in oflice 5. Then another two message two-way transmission trunk line 4|, similar to the trunk line 33, would be employed and a trunk cord circuit 42 would be utilized to extend the connection between the trunk line 4| and the trunk line 33 or a trunk circuit in the phantom group 34 may be employed. The cord circuit 43, similar to cord circuit 32, would be used to complete the call to the subscriber at 25.

The reference numeral ll represents the master generator in telephone ofiice l for developing alternating current signals, preferably twenty cycles per second, although other frequencies may be employed. These signals are supplied to the square wave amplifier 44 where they are changed into spaced square top pulses, and applied to the cord circuit 3| and other similar cord circuits in oifice I for controlling the message reducing and expanding mechanism to be fully explained later. These pulses from the square wave amplifier 44 are also applied to all relay equipments 23 and 38 to control signaling so that lamps will indicate the particular jack into which the cord circuit should be plugged. The alternating current control signals of sine wave form from the generator II are transmitted over the trunk I9 to the amplifier 45 in ofiice 4. From the amplifier 45 the signals are relayed over trunk 22 to the amplifier 45 in ofiice 5. In office 4 the signals from the amplifier 45 are also supplied to the square wave amplifier 41 and from this amplifier the square wave signals are applied to the relay equipments 29, 30 and 39 and cords 32 and 42. In office the signals from the amplifier 45 are supplied to the square wave amplifier 48 and from this amplifier the square top waves are applied to relay equipments 33 and cord 43.

In Figure 3 I have shown a pair of conductors 33 extending between two telephone ofiices l and 4 for the transmission and reception of two messages. This trunk may be considered as a two message or two party trunk line, and it is provided.

at either terminal with a pair of jacks, apparatus, and associated circuits for alternately including a pair of line relays or signal drop relays across the conductors to control each signal of a pair of signals alternately to notify the operator which jack or party should be answered.

In Figure 4, I have shown a phantom group of trunk circuits extending between two telephone ofiices l and 4 which may be used interchangeably with the trunk lines of Figure 3 for the transmission and reception of two messages simultaneously over each physical circuit 35 and 36 and two messages simultaneously over the phantom circuit 31. Each trunk circuit may be considered as a two message or two party circuit. The physical circuits and the phantom circuit are provided at either terminal with a pair of jacks, and apparatus for alternately including a pair of signal relays in a circuit inductively connected to the trunk conductors to control signals notifying the operator which jack or party should be answered in the phantom group.

Figures 5 and 6 show cord circuits for interconnecting subscribers lines and trunk lines. Figure 5 represents a cord circuit for connecting a subscribers line to a two message two-way transmission trunk circuit such as are shown in Figures 3 and 4. Associated with each cord is a message reducing and expanding mechanism for reducing the period of time for successive fragments of a message outgoing over the trunk, and for expanding the period of time for successive fragments of a message incoming from a trunk line.

Figure 6 represents a cord circuit for connecting to two double purpose trunk lines. This cord is different from the cord in Figure 5 in that the message reducing and expanding mechanism may be common to all the cord circuits in one operators position rather than being individual to each cord. In other words, since the period of time for the messages transmitted over both connected trunks has been reduced, the reducing and expanding mechanism is only used when the operator talks to either the calling or called party.

With further reference to Figure 3, the trunk conductors 33 terminate in a pair of jacks in parallel at either end for connecting two cord circuits to the same line for the transmission and reception of two different messages simultaneously. Jacks 49 and 53 may be known as the A party jacks and jacks 5| and 52 may be known as the B party jacks. Associated with each jack are line and cut off relays. The line relay 53 associated with jack 49 is adapted to be energized over conductors 33 by battery supplied from a connecting cord circuit at jack 50 and the out 01f relay 54 associated with jack 49 is energized through the sleeveconductor of jack 49 from battery in a connecting cord circuit to disconnect the line relay 53. Adapted to be operated in a like manner are the line relays 55, 55 and 57, and the cut off relays 58, 59 and 63, associated with the jacks 58, 5|, and 52 respectively. The cut oil relays 59 and 60 associated with the B party jacks are energized through resistors GI and 62 respectively to effect certain changes in the connecting cords, to be explained later. The energization of any line relay 53, 55, 56 or 5'! will cause its associated signal lamps 63, 64, 35 or 36 to glow, notifying the operator that a con nection is desired.

The master alternating current generator I! develops an output of sine wave form which is supplied to the square wave amplifier 44; the output from this amplifier may be equally spaced square top pulses which are applied to the signal control relay 6'! to alternately energize and deenergize the relay during equal periods of time. The relay 6'! in its deenergized position as shown in the drawing maintains a closed circuit through the line relay 53 at the contacts 58, and holds the circuit through line relay 55 open at contacts 69. The relay 6'! upon energizing holdsthe circuit through relay 53 open and maintains the circuit through relay 55 closed so that the line relays 53 and 59 are alternately placed in condition for energization over the trunk conductor's and for equal periods of time. Therefore the relays 55 and 55 may be energized through the cord circuits connecting jacks 59 and 52 respectively, to be more fully explained hereinafter.

The relay E9 in oilice 4 will be energized and deenergized in synchronism with the relay 8'! in oflice I, since the output of the master generator is also supplied over the trunk I9 to the amplifier'45 in office 4. The output from amplifier 45 is supplied to the square wave amplifier ll to develop spaced square form pulses in synchronism with the pulses from the amplifier 44. These pulses are applied to the signal control relay II] to thereby open and close the circuits through the line relays 55 and 51 at contacts 'II and I2 during equal periods of time. Therefore, the relays 55 and 5? may be energized through the cord circuits connecting jacks 49 and 5I respectively, to be further explained later.

With further reference to Figure 4 showing a phantom trunk group which may be one group of many between offices I and 8. The conductors 35 and 36 are the two physical circuits terminating in transformer or repeating coils windings I3, I4, 15 and I8. The phantom circuit is formed in a conventional manner by connections from the mid points of the repeating coil windings 13,14, I5 and I5 and terminating at both ends in other repeating coil windings "IT and 78 as shown in Fig. 4.

The terminal equipment '59 and 88 associated with each trunk circuit, comprises at each of fice terminal a pair of jacks connected to se arate repeating coil windings, a pair of line re lays, a pair of cut off relays, a signal control rel-a, and associated circuits for the transmission and reception of two different messages simultaneously over each physical circuit and at the same time two other messages over the phantom circuit, making a maximum of six simultaneous conversations over two pairs of conductors.

Jacks 8| and 82 associated with trunk conductors 35 may be known as the A party jacks, and jacks 83 and 84 may be known as the B party jacks- Associated with each jack are line and cut off relays. The line relay or drop signal 85 associated with the A party jack is adapted to be actuated by alternating current supplied from a connecting cord circuit at the A party jack 92, and the cut off relay 88 associated with jack 8I is energized through the sleeve conductor of jack 8! from battery in a connecting cord circuit to disconnect the relay 85. Adapted to be operated in like manner are the line or drop signal relays 81, 88 and 89, and the cut off relays 99, Ill and 92 associated with the jacks 82, 83 and 84 respectively. The relays ill and 92 are energized through resistors 93 and 94 to efiect certain changes in the connecting cords to be explained later. The energization of any line relay 85, 81, 88 or 89 will cause its associated signal lamp 95, 98, 91 or 98 to glow notifying the operator that a connection is desired. Spaced pulses from the square wave amplifier 48 are applied to the signal control relay 99 to alternately energize and deenergize the relay during equal periods of time. The relay 99 in its deenergized position maintains a closed circuit through the line relay 85 at the contacts I88, and holds the circuit through the line relay 88 open at contacts IIII. The relay 99 upon energizing holds the circuit through relay open, and maintains the circuit through relay 88 closed so that the line relays 35 and 88 are alternately placed in condition to be actuated by ringing current over the trunk conductors 35 for equal periods of time. Therefore, the relays 85 and 88 may be actuated by ringing current from the cord circuits connecting jacks 82 and 84 to be more fully explained later.

The relay I02 in orfice 4 will be energized and deenergized from spaced pulses supplied from the square Wave amplifier 41 in ofiice 4 to open and close the circuits through the line relays 81 and 89 at contacts I83 and I04 during equal periods of time. Therefore, the relays 81 and 89 may be actuated by signal current supplied through jacks 8| and 83. The relay I82 will be energized and deenergized in synchronism with the relays 99 and 6'! in office I since all control signals'are supplied by the master generator II. Similar terminal apparatus and circuits may be employed for the other physical circuit conductors 36 and also for the phantom circuit as shown in Fig. 4 by the blocks designated I9 and 89.

From the above description it has been shown that an operator may be signaled in either direction for the A and B parties over the phantom trunk group and also over the two conductor trunk.

Figure 5 shows a cord or link circuit for connecting either an individual or party telephone line with a multi party trunk line of Figure 3 or Figure 4 as illustrated in Figure 2 at 3| and 32, The cord circuit includes recording and reproducing mechanism for grouping and separating sound signals so that two cord circuits may be employed at each terminal of the trunk for carrying on two separate and private conversations over the trunk line at the same time.

The plug I is a calling or answering plug for the telephone lines, and plug I86 is a calling or answering plug for the trunk lines. Battery at I 81 is fed to the telephone line through resistance I98, secondary winding of transformer I99 winding III) of anti-sidetone transformer III. The operator may ring on the telephone line through the action of key H2, and she may talk to the subscriber by operating the key H3. The usual disconnect signal is provided at IM, which is caused to glow by the relay II5 returning to normal position when the subscriber on the connectedline hangs up his receiver. Battery at I I6 is fed over the trunk line through resistance II'I, conductors H8 and H9 when certain relays in the cord circuit are operated to be explained later, secondary winding of transformer I29, winding I2I of the anti-sidetone transformer I22, tip of plug I 06, trunk conductors of connected trunk line, ring of jack I68, to opposite side of the battery. A disconnect signal is provided. at I23 which may be actuated by the relay I24. The relay I24 is marginal and will not operate its armature in series with a line relay in the trunk circuit of Figure 3, but will be completely energized when a second cord circuit is connected to the opposite end of the trunk line of Figure 3, which may be like the cord circuit of Figure 5 except that the battery H6 would be connected opposite to that shown so that the two batteries in the connecting cord circuits would be in series. The disconnect signal I23 and relay I24 would not be used with the phantom group of trunks in Figure 4.

Assume that the plug I99 is connected to the A jack 49 in Figure 3: then relays 54, I25 and I26 would be energized in series over the sleeve conductors. Relay 54 upon energizing clears relay 53 from the trunk line; relays I 25 and I 26 upon energizing close a circuit from the square wave amplifier 44, conductor I21, Fig. 3, to conductor I21, Fig. 5, springs I28, springs I29 and I30,'to relay ISI. Therefore relay I3I is energized and deenergized during equal periods of time by the spaced pulses from the amplifier 44. Relay I3I in its normal or deenergized position shorts the very high resistance I32 over conductor H8, springs I 33, springs I34, conductor H9. The duration of this condition may be considered one talking period for the A party. Relay 55 in the trunk circuit will be energized during this period or during the time that relays I3I and I are deenergized to notify the operator at 64 that a connection is desired. The ringing key I35 is not used with the two conductor trunks. Relay I3I during the period that it is energized opens the contact springs I35 to include the resistance I32 in the battery circuit feeding the trunk line, thereby rendering the cord circuit inoperative or blocked to sound signals, which may be known as a B party talking period. Since the control signals are in synchronism, relays I0 and I3I will be operated in unison and line relay 55 will be cleared from the trunk lin during the B party talking period.

In order that two telephone messages may be transmitted over the trunk line, I reduce the interval of portions or fragments of each message by approximately one half and transmit these grouped portions in alternate periods of time. Therefore, by recording the sound signals from the telephone line or the operator's telephone set on a magnetic Wire or tape and reproducing the signals by a coil traveling in the opposite direction to that of the wire and at approximately the same speed, the interval for each portion will be reduced or the frequency of the signals will be increased.

The sound signals from a connected telephone line would pass through winding I I0 and the alternating current component seeking the path of least resistance would pass through winding I36 and I3? of theanti-sidetone transformer III, condenser L38 to ring conductor. The primary winding of audio transformer I39 bridged across the winding I66 of the anti-sidetone transformer will vary the potential on grid I40 of the amplifier tube I ll in accordance with sound signals received from the telephone line. The anode output of tube I4I may be applied through the transformer I42 t0 the stationary recording coil I43 for recording the signals magnetically on the moving wire or tape I44.

In the recording and reproducing mechanism I preferably employ an endless wire I44 of small diameter traveling in the direction indicated by the arrows over the pulleys I45, I46, I41, I48, I49 and I50. The pulley I46 is driven at a uniform speed by a motor I52 through the friction clutch indicated by the dashed circle II connected to the shaft I53. Attached to the pulley I48 is a disk of larger diameter I54, driving the member I55 on the slide bars I56 and I5? in a reciprocat ing motion through the action of the connecting arm I58 attached near the rim of the disk I54 so that the distance traveled right to left by the member I55 is approximately equal to the distance traveled by the wire in one half revolution of the pulley and disk I48 and I54.

The signals recorded on the wire I44 by the coil I43 may be picked up by the reproducing coil I59 traveling from right to left or in a direction reverse to that of the wire so that the signals will be reproduced in the coil I59 in one half of the interval that was required to record them on the wire. The coil I59 traveling from left to right moves very nearly at the same speed and in the same direction as the wire. Therefore the coil I59 would be inactive and as will be shown later the signals would be blocked in the cord circuit during the left to right movement of the coil.

The signals reproduced by the coil I59 are applied to the grid I60 of the amplifier tube I6I. The output of tube I6I is applied to the primary winding of transformer I20 to vary the current supplied by battery II6 to the trunk line over a path as previously described. Therefore, it has been shown that the sound signals from the subscribers line may be separated into small portions, and grouped by the interval being reduced through the reciprocating action of the coil I59, and then transmitted over the trunk line in spaced periods of time. As shown in Figure 2 another cord circuit 32 may be employed in office 4 to connect a telephone line with the A jack of the trunk line. This cord circuit as previously stated may be exactly like the cord circuit of Figure 5 except that the terminals of battery Il6 may be reversed. Therefore, signals originating in office 4 and transmitted over the trunk line would also be in spaced groups and the alternating current component would flow through windings I2I, I62 and IE3 of the anti-sidetone transformer I22, condenser I64 to the opposite side of the line. The primary winding of transformer I65 bridged across the winding I62 will causethe potential on the grid I66 of amplifier I67 to vary in accordance with the sound signals received from the trunk line. The anode output of tube I67 is applied through the audio transformer I68 to the recording coil I69 mounted on the member I and traveling forward and backward along the wire I44 to record sound signals thereon durin the right to left movement of the coil only.

' The coil travels left to right in the same direction and approximately the same speed as the wire, therefore no signals would be developed. Furthermore the cord circuit will be blocked during this period by including the resistor I32 in the battery supply circuit. The coil I69 in moving right to left along the wire I44 in a direction opposite to the movement of the wire will cause the signals to be recorded over a length of the wire I44 equal to approximately twice the distance that the coil I69 travels right to left, so

that the signals received over the trunk line will be expanded to their normal interval and reproduced in the stationary coil I10 and applied to the grid III of the amplifier tube I72. The anode output of the tube I12 may be applied to the primary winding of the transformer I09 to vary the current in the telephone one line over a path as previously described.

The coils I76 and H4 are high frequency erasing coils for restoring or demagnetizing the wire I44 so that further messages may be recorded thereon.

The pole pieces for the recording and reproducing coils are provided with a narrow slot for the wire I44 to travel through.

The A partly talking periods over the trunk line are the periods between synchronizing pulses, and the B party talking periods are during the intervals of the synchronizing pulses, which are the same in each two party trunk throughout the esta es '9 system hr"Wo1- si na s g na n i ofiice I and transmitted over A party trunk would be transmitted during the intervals between control pulses and the answer from a subscriber in ofiice I would also be transmitted during the intervals between control pulses.

In order to synchronize the grouping and separating'mechanism with the proper party A or B on the trunk line, I provide holding or retarding magnets I15 and I16 for holding the disk I54 so that the member I55 will be held or retarded until a control pulse is received. The magnet I15 may be considered the A party holding magnet and in its nonoperated position as shown in the drawing it holds the disk I56 from rotating by the armature bar I11 engaging the pin I18 in the disk I59. As soon as a control pulse is received over conductor I21, the, magnet I15 is energized in parallel with relay I3! through springs I28, I29 and I30, and conductor I19, durin the intervals of the control pulses to permit the disk I54 to rotate. The motor is arranged to drive the disk a little faster than one revolution per cycle of the control signals so that the bar I11 will slightly retard the disk just before the control pulse is received. The magnet I16 is continuously energized while the plug I06 is connected to the A party jack through the springs I80, I61 and I82 and conductor I83, to hold its armature bar I64 out of engagement with pin I85.

From the above it has been shown that the member I55 will move from right to left while the relay ISI is deenergized to transmit sound sig nals during the intervals between control pulses, and that during the intervals of the control signals the cord circuit is blocked by including the resistance I32 in the talking path. As previously explained another cord circuit similar to Figure will be employed in office 4 so that a subscriber in ofiice I and a subscriber in ofiice 4 may talk over the A party trunk line. A second subscriber in office I may talk to a second subscriber in oflice 4 at the same time over the B party trunk line. In which case another cord circuit similar to Figure 5 would be connected tot he B jack 5| in office I, and a similar cord circuit would be connected to the B jack 52 in office I.

Inserting the plug I06 into the B jack 5I will cause relays 59 and I26 to be energized through the resistance BI over the sleeve conductors, relay I25 is arranged so that its armature will not be operated when the resistor 6| is included in its energizing circuit. Therefore relay I86 will be energized intermittently by the control signals over conductor I21, and through the springs I28, I29 and I81 to the relay I86. Relay I66 during its energized position may be considered the B party talking period and the resistor I32 is shorted at springs I88 during the intervals of the control pulses, and in the intervals between pulses the resistor I32 is included in the talking path to block the signals and to reduce the current drain. Instead of using the resistor 32 the talking path could be opened and closed by the relay I86. The holding magnet I16 will be operated in unison with the relay I86 over conductor I83 and springs I29 and I28, to retard the rotation of the disk I 59 by the armature arm I 84 engaging the pin I85, which places the member I55 in position to start moving to the left at the instant a control signal is received. ,Holding magnet I is held in its operated position when; the cord is used with B party trunk lines, over conductor I19 through springs I89, IBI and I80 I to ground. The re! m inde f he a a s, d a soc a ed ci cuit 10 in the cord functions a described in connection with the A party.

From the above it, has been shown that two private conversations may be carried on over a two conductor trunk line by grouping the signals in alternate spaced periods, and also that the operator may be signaled in either direction. It is also shown that the cord circuit of Figure .5 may be used for either A or B connections.

The cord circuit of Fi ure 5 may be. used with the phantom trunk group of Figure 4 in the same manner as above described except to signal the distant operator. The ringing key I35 would be operated, which causes ringing current to be sent out over the trunk line during a period depending upon which party jack is used. Should plug I66 be inserted in theA jack 8| then ringing current will only be supplied to the trunk line during the A party intervals, through springs I and NH, and when the plug I06 is connected to 3 jack 8,3 ringing current will only be supplied to the trunk during the B party interval through the contacts I92. The motor circuit may be closed by the springs I93 actuated by the relay I26.

The cord circuit for connecting two trunks is illustrated at 42 in Figure 2 and is shown in more detail in Figure 6. The principal difference between this cord circuit and that of Figure 5-, is that the signal grouping and separating mechanismin Figure 6 is common to an operator's position in the switchboard rather than being in: dividual to each cord circuit. The operation. is very similar to that. describing, Figure 5.

The plug I96 may be considered the answering plug and the plug I91 may be the callingplug. Battery at I98 is fed through the windings of the repeating coil I99 to the tip and ring conductors of both the answering and calling plugs. Disconnect signals are provided at 200 and 2M adapted to be operated by the relays. 202 and 203, when the cord at the opposite terminalof the connected trunks are withdrawn restoring .therelays to normal position. The relays will not remain operated in series with a trunk line relay, but may be operated by current from two cord circuit batteries.

Assuming that plug I96 is connected to an A party trunk inanswer to a signal then relays 204 and 205 will be energized over the sleeve conductor in series with the associated cut offrelay to apply spaced control pulses from the square wave amplifier over conductor 206, springs 201, 208 and 209 tothe re1ay2l0. Relay 2I0 in its nonoperated position .which may be considered the talking condition for the A party trunk line, shorts the high resistance-2l I, and when operated springs 2I2 are opened to include the resistor 2 in the talking path so that negligible current will flow during the B party trunk line interval. Should th plug I96 be connected to a B party jack the armature of relay 204 would not be operated on account of. a resistor in series with the cut off relay in all B party trunks. Therefore relay 2I3 would be energized by control pulses over conductor 206, springs 201, 208 and 2M, which will short the resistor 2 when energized or during the intervals of the control pulses.

From the above it has been shown that the talking periods for the A and'B party are the same as described for the cord circuit of Figure 5.

The operator in order to obtain information over the trunk line must operate the key 2I5 to connect ;her telephone set with the line which compriseswire recording. and reproducing mechs- 1 163 f separating the grouped signals from 11 the trunk line and expanding their intervals to normal, and for grouping the signals from the operators microphone to transmit them over the trunk line,

The path for the grouped sound signals from the trunk line may be over the tip conductor, winding 2I5, 2I'I and H8 of the anti-sidetone transformer 2 l9, condenser 220, to the ring conductor. The signals in the coil 2 I! are applied to the grid of 22I through the transformer 222. The anode output of tube 22I is applied through the transformer 223 to the movable recording coil 224 for recording the sound signals on the wire 225 when the coil is traveling from right to left. The wire 225travels around the several pulleys as indicated by the arrows and this mechanism issimilar to that described in Figure 5. A motor 226 drive the disk 22'! and pulley 228 through a friction clutch 229 indicated by the dashed circle. The member 230 is driven in a reciprocating motion through the action of arm 23I.

The signals recorded on the wire by coil 224 are picked up by the reproducing coil 232 and applied to the grid of tube 233, the output being applied through transformer 234 to the operators receiver 235.

The sound signals originating at the operators microphone 236 are applied through transformer 23! to the grid of tube 238. After suitable amplification in this tube they are applied to the stationary recording coil 239 through the transformer 240. The signals recorded on the wire 225 are picked up by the reproducing coil 24! mounted on member 230 in its movement from right to left opposite to the direction of the moving Wire so that the signals are grouped into approximately one-half their normal interval. These grouped signals are applied to the grid of tube 242 to vary the current from the battery I98 through the transformer 243 and winging 2 I 6 of the anti-sidetone transformer, andwindings of the repeating coil I99.

The control magnet 244 for the A party is intermittently energized by the control signals from conductor 266 through springs 2M, and 268, conductors 245 and 246, during the time that key 2 I5 is operated, The control magnet 24'! may be energized continuously when the cord circuit is used for *the A party from ground through springs 248, 249 and 250, conductors 25I and 252. The control magnet 24'! controls the rotation of the disk 22'! when the cord circuit'is used with a B party jack by the control signals through springs 201, 268 and 2I4, conductors 25I and 252. Likewise the magnet 244 is continuously energized when the cord circuit is used for the B party from ground through springs 248, 249 and 253, conductors 245 and 246.

Relays 254 and 255 are energized over the sleeve conductor When the cord circuit is connected to the A party jacks and relay 254 only is energized when connected to the B party jack as explained for the opposite end of the cord circuit. Should the operator insert the plug I97 into the Wrong party jack the relay 256 will be energized to open the cord circuit at springs 25'! and 258 and also light the signal lamp 259 to notify the operator of the mistake. For instance, should plug I91 be inserted in B party jack when plug I96 is connected to an A party jack, then relay 256 would be energized from ground through springs 25!! and 26I, at relay 264, springs 262, 263 and 264. Should plug i9! be connected to A party jack when plug I96 is in B jack then relay 256 would 12 be energized from ground through springs 26!), 265, 236, 263 and264.

The operator may ring out over the trunk line in spaced intervals by operating the key 261. The A party ringing current is. supplied from the generator 268 through springs 269 and 279 during the deenergization periods of relay 2I9. The B party ringing current is supplied from the generator 263, springs 2'II during the energized periods of relay 2I3.

From the above it has been shown that two twoparty trunk lines may be connected together by two trunk cord circuits for transmitting the sound signals for two private conversations by grouping the signals from both messages in successive rotation.

In the various circuits shown and described I have simplified the drawings by indicating the source of potential by a positive or negative sign. Also I have omitted the heater element from the various tubes.

The embodiments of the invention which have been given herein are illustrations of how the various features may be accomplished and of the principles involved. It is to be understood that the invention contained herein is capable of embodiments in other forms and adaptations, withi out departing from the spirit of the invention and I from the subscriber's line into equal portions, and

for reducing the interval of each portion to transmit over said trunk line.

2. In a telephone system, a subscribers line terminating in a jack, a trunk line terminating in a jack, a cord circuit for connecting said subscribers line jack to said trunk line jack, and means in said cord circuit for expanding the interval of spaced portions of electrical signals representative of sound received oversaid trunk line, and for transmitting successive portions of said expanded signals over said subscribers line.

3. In a telephone system, a subscribers line terminating in a jack, a trunk line terminating in a jack, a cord circuit for connecting said subscribers line jack to said trunk line jack, and frequency changing means in said cord circuit for grouping and expanding electrical signals representative of messages received from said subscribers line and said trunk line to transmit the grouped signals over said trunk line and to transmit the expanded signals over said subscribers line.

4. In a telephone system, a subscribers line terminatingin a jack, a trunk line terminating in a jack, a cord circuit for connecting said subscribers line jack to said trunk line jack, means in said cord circuit to group electrical signals representative of a message received from said subscribers line, and for transmitting these grouped signals over said trunk line, and means in said cord circuit to expand the interval of spaced portions of electrical signals representative of sound received over said trunk line, and for transmitting the expanded'signals over said subs-cribers line.

5. In a telephone system, a trunk line, a cord circuit adapted to be removably connected to said line, said cord circuit comprising frequency changing mechanism for grouping and expand- 13 ing signals representative of messages for the transmission and reception of the signals in spaced periods of time over said line.

6. In a telephone system, a plurality of telephone lines, a two conductor trunk line, a pair of cord circuits adapted to interconnect at least any two of said telephone lines to said trunk line, said cord circuits comprising frequency changing mechanisms for grouping and expanding signals representative of different messages to transmit the signals from the said two telephone lines in successive rotation over the trunk line.

7. In a telephone system, a telephone line, a trunk line, a cord circuit for removably connect ing the telephone line with the trunk line, said cord circuit comprising mechanism for recording signals representative of a telephone message received over said telephone line, and for separating, and reproducing the said signals at a higher frequency in spaced groups for transmission over said trunk line.

8. In a telephone system, a first trunk line, and a second trunk line, a plurality of interchangeable cord circuits for electrically interconnecting both trunk lines, mechanism common to said cord circuits for recording spaced groups of message signals received over either of said trunk lines and for reproducing said recorded signals in expanded intervals, and a key in each of the said cord circuits for electrically connecting said mechanism to its associated cord circuit.

9. In a telephone system, a first telephone ofiice, and a second telephone ofirce, subscribers lines terminating in each of the said oflices, a two party trunk line connecting both of said offices, a pair of cord circuits in the first office provided with removable plugs for connecting two subscribers lines to the trunk line, and a pair of cord circuits in the second office provided with removable plugs for connecting two other subscribers lines to the trunk line for two simultaneous conversations between subscribers in the first and second offices, each of said cord circuits comprising frequency changing mechanism for grouping signals representative of a telephonic message to transmit the signals over said trunk line in spaced periods of time.

10. In a telephone system, a first trunk line, extending from a first ofiice to a second ofiice, terminating in at least a first and a second jack in the first ofiice, a subscribers line terminating in a jack in the first office, means in said first ofiice to produce central impulses, a cord circuit in said first ofiice for connecting said subscribers line jack to any one of said trunk line jacks, means in said cord circuit under control of said impulses to select portions of electrical signals representative of a telephone message received from said subscriber's line to transmit the signals over said trunk line during certain recurrent periods of time, or during other recurrent periods of time according as the said cord circuit is connected to said first trunk line jack or said second trunk line jack, a second trunk line extending between the first and second offices, means to transmit said control impulses over said second trunk line, a telephone line in the second office, a link circuit in the second office for interconnecting said first trunk line and said telephone line, and means in said link circuit under control of the received control impulses to select said spaced periods to receive the said electrical signals for transmitting the signals over said telephone line.

JOHN H. HOMRIGHOUS.

REFERENCES CITED The following references are of record in the file of this patent:

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